The present invention relates to a method for diacylaminoalkylating a cross-linked polymer of a monovinylidene aromatic compound and to methods for preparing ion exchange resins from the diacylaminoalkylated polymer.
Ion exchange resins are normally solid materials which have the ability to exchange ions in a liquid solution without substantial alteration of the solid resin's structure. For this reason, they are widely used in recovery processes such as the recovery of uranium and in waste treatment such as removing undesirable components from water.
Conventionally, many ion exchange resins are prepared by attaching active ion exchange groups to a cross-linked polymer of a monovinylidene aromatic. For example, an anion exchange resin is conventionally prepared by the aminoalkylation of said polymer. Typically, said aminoalkylation consists of the sequential steps of chloromethylation, amination and, if desired, alkylation. See, for example, Ion Exchange, by F. Helfferich, published in 1962 by McGraw-Hill Book Company, New York. Chloromethyl methyl ether is conventionally employed for such chloromethylation. Unfortunately, bischloromethyl ether, which in a recent New York University Medical Center report has been linked to bronchogenic cancer in rats, is commonly present in small amounts in the chloromethyl methyl ether.
Alternate methods for aminoalkylating an aromatic polymer which do not involve the use of chloromethyl methyl ether have been proposed for preparing anion exchange resins. For example, U.S. Pat. No. 3,006,866 to Corte and Netz discloses that a cross-linked polymer of a monovinylidene aromatic is aminoalkylated by (1) the condensation reaction of the cross-linked aromatic polymer and a preformed N-(haloalkyl)imide, e.g., N-chloromethyl succinimide, in the presence of a swelling agent and a Friedel-Crafts catalyst and (2) the hydrolysis of the resulting reaction product. Unfortunately, the condensation reaction liberates highly corrosive hydrogen halides, e.g., HCl, and requires elevated temperatures. A similar method of aminoalkylation which does not liberate hydrogen halide is presented in U.S. Pat. No. 3,925,264 to Corte, Heller and Netz wherein a preformed N-(hydroxyalkyl)imide is employed in place of the N-(haloalkyl)imide. Unfortunately, said process requires the undesirable step of removing water during the condensation reaction. Moreover, the preparation of the preformed N-(haloalkyl)imide or N-(hydroxyalkyl)imide in said methods requires the undesirable expenditures of substantial time and apparatus.
In view of the stated deficiencies of the prior art methods for aminoalkylating an aromatic polymer, it remains highly desirable to effectively prepare anion exchange resins by a method which does not involve the use of chloromethyl methyl ether.